Render audio button function and use
The render audio button combines all of the audio tracks that have been created in the video sequence editor into one audio file. This is useful if, say you had an animation that had multiple sounds in it but you rendered it as an image sequence and plan to put the output sequence in another project as part of a compilation. Say you forgot that you were going to create all the audio in the compilation. Instead of putting in the numerous audio tracks in again trying to put them in the perfect place again, you could render the audio from the first project and put it in the second project parallel to the matching image sequence. Also, it probably works appropriately with the speaker object, but I'm not sure at all. I've never tried. ;)

There's a simple example. I probably could have thought of something more realistic, but I hope that helps!